1. Field of Invention
The present invention relates in general to electric motors, and more particularly to electric motors of a two rotor single stator type which comprises two rotors which rotate relative a single common stator. More specifically, the present invention is concerned with the electric motors of a type which has an improved supporting structure for the single common stator.
2. Description of Related Art
One electric motor of the above-mentioned type is shown in Japanese Patent First Provisional Publication (Tokkai) 2000-14086. In the electric motor of this publication, upon feeding a compound electric current to a stator, two rotors, that is, inner and outer rotors are rotated relative to a common stator. By controlling the compound electric current fed to the stator, rotation of the inner rotor and that of the outer rotor are individually controlled. In this electric motor, the stator and the two rotors are all cylindrical in shape and housed in a case, and the inner and outer cylindrical rotors are concentrically disposed in and about the cylindrical stator respectively.
In the electric motor of the publication, for transferring rotation of the outer rotor to an external driven member, the outer rotor has an output part that extends diametrically across one axial end of the stator. Both the output part and the outer rotor thus rotate together like a single unit. Thus, in the electric motor of this publication, one axial end of the stator over which the output part of the outer rotor diametrically extends can not be used as a supported portion of the stator due to obstruction by the output part of the outer rotor. Accordingly, supporting of the stator relative to the case has to be made by only the other axial end of the stator, which however tends to induce a complicated and costly supporting structure for the stator. In addition, the complicated supporting structure tends to make a cooling system of the stator complicated. Furthermore, since the space for receiving the stator directly depends on the diameter of the outer rotor, enlargement of the stator is not easily achieved.
It is therefor an object of the present invention to provide an electric motor of two rotor single stator type, whose stator supporting structure is free of the above-mentioned shortcomings.
According to a first aspect of the present invention, there is provided an electric motor which comprises a case; a cylindrical stator which is installed in the cylindrical case; first and second discal rotors which are installed in the case and arranged at axially opposed end portions of the cylindrical stator respectively to rotate about an axis of the cylindrical stator; and a case bracket which is installed in the case to support the cylindrical stator relative to the case, the case bracket being in abutment with an inner surface of the case to be held in the case.
According to a second aspect of the present invention, there is provided electric motor which comprises a cylindrical case; a cylindrical stator which is concentrically installed in the cylindrical case, said stator having a cylindrical center bore; first and second discal rotors which are installed in the cylindrical case and respectively arranged at axially opposed end portions of the cylindrical stator to rotate about a common axis; a hollow output member having the second discal rotor concentrically mounted thereon; an output shaft passing through the cylindrical center bore of the cylindrical stator and having one end portion on which the first discal rotor is concentrically mounted and the other end around which the hollow output member is concentrically disposed keeping a cylindrical space therebetween; and first and second annular bracket members which are tightly and concentrically disposed in the cylindrical case in a manner to put therebetween the cylindrical stator to hold the cylindrical stator relative to the cylindrical case.